Re: [PATCH v1] drm/xe: Drop dma mappings for wedged device

[Raag Jadav <raag.jadav@intel.com>]

On Tue, Mar 24, 2026 at 12:52:30PM +0000, Matthew Auld wrote:
> On 24/03/2026 07:13, Raag Jadav wrote:
> > As per uapi documentation[1], the prerequisite for wedged device is to
> > drop all dma mappings. Reuse xe_bo_pci_dev_remove_pinned() for this,
> > which iterates over external bo list and removes all dma mappings.
> > 
> > [1] Documentation/gpu/drm-uapi.rst
> 
> Can you point to where it says that? Do you just mean the: "disabling DMA to
> system memory" ?
> 
> One other thing that maybe jumps out is:
> 
> "All existing mmaps should be invalidated and
> page faults should be redirected to a dummy page"
> 
> Are we also missing that? We have the dummy page flow, but do we actually
> force everything to be refaulted?

I tried this with commit c020fff70d75 but it clearly doesn't cover
everything.

> Something like:
> 
>  /* Clear all CPU mappings pointing to this device */
>  unmap_mapping_range(dev->anon_inode->i_mapping, 0, 0, 1);

Sure.

> > Signed-off-by: Raag Jadav <raag.jadav@intel.com>
> > ---
> > PS: This is pretty much uncharted territory for me, so please consider
> > this an RFC.
> > 
> >   drivers/gpu/drm/xe/xe_bo_evict.c | 8 +++++++-
> >   drivers/gpu/drm/xe/xe_bo_evict.h | 1 +
> >   drivers/gpu/drm/xe/xe_device.c   | 2 ++
> >   3 files changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_bo_evict.c b/drivers/gpu/drm/xe/xe_bo_evict.c
> > index 7661fca7f278..f741cda50b2d 100644
> > --- a/drivers/gpu/drm/xe/xe_bo_evict.c
> > +++ b/drivers/gpu/drm/xe/xe_bo_evict.c
> > @@ -270,7 +270,13 @@ int xe_bo_restore_late(struct xe_device *xe)
> >   	return ret;
> >   }
> > -static void xe_bo_pci_dev_remove_pinned(struct xe_device *xe)
> > +/**
> > + * xe_bo_pci_dev_remove_pinned() - Unmap external bos
> > + * @xe: xe device
> > + *
> > + * Drop dma mappings of all external pinned bos.
> > + */
> > +void xe_bo_pci_dev_remove_pinned(struct xe_device *xe)
> >   {
> >   	struct xe_tile *tile;
> >   	unsigned int id;
> > diff --git a/drivers/gpu/drm/xe/xe_bo_evict.h b/drivers/gpu/drm/xe/xe_bo_evict.h
> > index e8385cb7f5e9..6ce27e272780 100644
> > --- a/drivers/gpu/drm/xe/xe_bo_evict.h
> > +++ b/drivers/gpu/drm/xe/xe_bo_evict.h
> > @@ -15,6 +15,7 @@ void xe_bo_notifier_unprepare_all_pinned(struct xe_device *xe);
> >   int xe_bo_restore_early(struct xe_device *xe);
> >   int xe_bo_restore_late(struct xe_device *xe);
> > +void xe_bo_pci_dev_remove_pinned(struct xe_device *xe);
> >   void xe_bo_pci_dev_remove_all(struct xe_device *xe);
> >   int xe_bo_pinned_init(struct xe_device *xe);
> > diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
> > index 207ad2eea412..ac51b04560df 100644
> > --- a/drivers/gpu/drm/xe/xe_device.c
> > +++ b/drivers/gpu/drm/xe/xe_device.c
> > @@ -1351,6 +1351,8 @@ void xe_device_declare_wedged(struct xe_device *xe)
> >   	for_each_gt(gt, xe, id)
> >   		xe_gt_declare_wedged(gt);
> > +	xe_bo_pci_dev_remove_pinned(xe);
> 
> AFAIK this just removes the iommu mappings for kernel BOs (small subset of
> BOs), if there are any. Also if you are not using iommu, then dma between
> GPU and system memory is still possible. And for userspace BOs nothing
> changes. But I guess this is still better than nothing and will maybe catch
> some misuse?

Yeah, I just floated this to start the discussion. Thanks for the pointers,
will explore this.

Raag

> >   	if (xe_device_wedged(xe)) {
> >   		/*
> >   		 * XE_WEDGED_MODE_UPON_ANY_HANG_NO_RESET is intended for debugging
>